Electrophotographic photosensitive member and process for production thereof

ABSTRACT

A layer of amorphous silicon containing H, preferably 10-40 atomic % H, is used as a photoconductive layer for electrophotographic photosensitive member.

This application is a division of the Rule 1.62 continuation ofapplication Ser. No. 08/440,123, filed May 23, 1995, now U.S. Pat. No.5,585,149, which in turn is a continuation of application Ser. No.08/351,561 filed Dec. 7, 1994, now abandoned, which is a continuation ofapplication Ser. No. 07/795,249, filed Nov. 18, 1991, now abandoned;which is a continuation of application Ser. No. 07/782,098, filed Sep.30, 1985, now abandoned; which is a division of application Ser. No.695,428, filed Jan. 28, 1985, now U.S. Pat. No. 4,552,824; which is acontinuation of application Ser. No. 449,842, filed Dec. 15, 1982, nowabandoned; which is a division of application Ser. No. 214,045, filedDec. 8, 1980, now U.S. Pat. No. 4,451,547; which is a division ofapplication Ser. No. 971,114, filed Dec. 19, 1978, now U.S. Pat. No.4,265,991.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to an electrophotographic photosensitive memberused for forming images by using electromagnetic waves for example,ultraviolet rays visible ray, infrared ray, X ray, gamma ray and thelike, and a process for preparing the photosensitive member.

2. Description of the Prior Art

Heretofore, there have been used inorganic photoconductive materialssuch as Se, CdS, ZnO and the like and organic photoconductive materialssuch as poly-N-vinyl-carbazole trinitrofluorenone and the like as aphotoconductive material. for photoconductive layers ofelectrophotographic photosensitive members.

However, they are suffering from various drawbacks.

For example, Se has only a narrow spectral sensitivity range, and whenthe spectral sensitivity is widened by incorporating Te or As, the lightfatigue increases. Se, As and Te are harmful to man. When Sephotoconductive layers are subjected to a continuous and repeatingcorona discharge, the electric properties are deteriorated, Sephotoconductive layers are of poor solvent resistance. Even if thesurface of an Se photoconductive layer is covered with a surfaceprotective coating layer, the problems are not sufficiently solved.

Se photoconductive layers may be formed in an amorphous state so as tohave a high dark resistances but crystallization of Se occurs at atemperature as low as about 65° C. so that the amorphous Sephotoconductive layers easily crystallize during handling, for example,by ambient temperature or friction heat generated by rubbing with othermembers during image forming steps, and the dark resistance is lowered.

ZnO and CdS are usually mixed with and dispersed in an appropriateresinous binder. The resulting binder type photoconductive layer is soporous that it is adversely affected by humidity and its electricproperties are lowered and further developers enter the layer resultingin lowering release property and cleaning property. In particular, whena liquid developer is used, the liquid developer penetrates the layer toenhance the above disadvantages, CdS is poisonous to man. ZnO bindertype photoconductive layers have low photosensitivity, narrow spectralsensitivity range in the visible light region, remarkable light fatigueand slow photoresponse.

Electrophotographic photosensitive members comprising organicphotoconductive materials are of low humidity resistance, low corona ionresistance, low cleaning property, low photosensitivity, narrow range ofspectral sensitivity in the visible light region and the spectralsensitivity range is in a shorter wave length region. Some of theorganic photoconductive materials cause cancer.

In order to solve the above mentioned problems, the present inventorshave researched amorphous silicon (hereinafter called "a-Si") andsucceeded in obtaining an electrophotographic photosensitive member freefrom these drawbacks.

Since electric and optical properties of a-Si film vary depending uponthe manufacturing processes and manufacturing conditions and thereproducibility is very poor (Journal of Electrochemical Society, Vol.116, No. 1, pp 77-81, January 1969). For example, a-Si film produced byvacuum evaporation or sputtering contains a lot of defects such as voidsso that the electrical and optical properties are adversely affected toa great extent. Therefore, a-Si had not been studied for a long time.However, in 1976 success of producing p-n junction of a-Si was reported(Applied Phisics Letter, Vol. 28, No. 2, pp. 105-7, 15 Jan. 1976). Sincethen, a-Si drew attentions of scientists. In addition, luminescencewhich can be only weakly observed in crystalline silicon (c-Si) can beobserved at a high efficiency in a-Si and therefore, a-Si has beenresearched for solar cells (for example, U.S. Pat. No. 4,064,521.

However, a-Si developed for solar cells can not be directly used for thepurpose of photoconductive layers of practical electrophotographicphotosensitive members.

Solar cells take out solar energy in a form of electric current andtherefore, the a-Si film should have a low dark resistance for thepurpose of obtaining efficiently the electric current at a good SN ratio[photo-current (Ip)/dark current (Id)], but if the resistance is so low,the photosensitivity is lowered and the SN ratio is degraded. Therefore,the dark resistance should be 10⁵ -10⁸ ohm·cm.

However, such degree of dark resistance is so low for photoconductivelayers of electrophotographic photosensitive members that such a-Si filmcan not be used for the photoconductive layers.

Photoconductive materials for electrophotographic apparatuses shouldhave gamma value at a low light exposure region of nearly 1 since theincident light is a reflection light from the surface of materials to becopied and power of the light source built in electrophotographicapparatuses is usually limited.

Conventional a-Si can not satisfy the conditions necessary forelectrophotographic processes.

Another report concerning a-Si discloses that when the dark resistanceis increased, the photosensitivity is lower. For example, an a-Si filmhaving dark resistance of about 10¹⁰ ohm·cm shows a loweredphotoconductive gain (photocurrent per incident photon). Therefore,conventional a-Si film can not be used for electrophotography even fromthis point of view.

Other various properties and conditions required for photoconductivelayers of electrophotographic photosensitive member such aselectrostatic characteristics, corona ion resistance, solventresistance, light fatigue resistance, humidity resistance, heatresistance, abrasion resistance, cleaning properties and the like havenot been known as for a-Si films at all.

The present inventors have succeeded in producing a-Si film suitable forelectrophotography by a particular procedure as detailed below.

SUMMARY OF THE INVENTION

An object of the present invention is to provide an electrophotographicphotosensitive member and a process for preparing theelectrophotographic photosensitive member, the process being able to becarried out in an apparatus of a closed system to avoid the undesirableeffects to man and the electophotographic member being not harmful toliving things as well as man and further to environment upon the use andtherefore, causing no pollution.

Another object of the present invention is to provide anelectrophotographic photosensitive member which has moisture resistance,thermal resistance and constantly stable electrophotographic propertiesand is of all environmental type, and a process for preparing theelectrophotographic photosensitive member.

A further object of the present invention is to provide anelectrophotographic photosensitive member which has a high light fatigueresistance and a high corona discharging resistance, and is notdeteriorated upon repeating use, and a process for preparing saidmember.

Still another object of the present invention is to provide anelectrophotographic photosensitive member which can give high qualityimages having a high image density, sharp half tone and high resolution,and a process for preparing said member.

A still further object of the present invention is to provide anelectrophotographic photosensitive member which has a highphotosensitivity, a wide spectral sensitivity range covering almost allthe visible light range and a fast photo-response properties, and aprocess for preparing said member.

Still another object of the present invention is to provide anelectrophotographic photosensitive member which has abrasion resistance,cleaning properties and solvent resistance and a process for preparingsaid member.

According to one aspect of the present invention, there is provided aprocess for preparing an electrophotographic photosensitive member whichcomprises:

(a) evacuating a pressure-reducible deposition chamber to reduce thepressure,

(b) heating a substrate for electrophotography disposed in a fixedposition in said deposition chamber to 50°-350° C.,

(c) introducing a gas containing a hydrogen atom as a constituent atominto said deposition chamber,

(d) causing electric discharge in space of said deposition chamber inwhich at least one of silicon and a silicon compound by electric energyto ionize said gas, and

(e) depositing amorphous silicon on said substrate at a deposition rateof 0.5-100 angstroms/sec. by utilizing said electric discharge whileraising the temperature of said substrate from the starting temperature(T₁), to form an amorphous silicon photo-conductive layer of apredetermined thickness.

According to a further aspect of the present invention, there isprovided a process for preparing an electrophotographic photosensitivemember which comprises:

(a) evacuating a pressure-reducible deposition chamber to reduce thepressure,

(b) heating a substrate for electrophotography disposed in a fixedposition in said deposition chamber to 50°-350° C.,

(c) introducing a gas containing a hydrogen atom as a constituent atominto said deposition chamber,

(d) causing electric discharge in a space of said deposition chamber inwhich at least one of silicon and a silicon compound by electric energyto ionize said gas,

(e) depositing amorphous silicon on said substrate at a deposition rateof 0.5-100 angstroms/sec. by utilizing said electric discharge whilecontinuing the electric discharge for a period of time sufficient toform an amorphous silicon photoconductive layer of a predeterminedthickness, and

(f) while forming said amorphous silicon photoconductive layer, raisingthe temperature of said substrate from the starting temperature (T₁) toa temperature (T₂) and then decreasing the temperature to a temperaturelower than the temperature (T₂).

According to a further aspect of the present invention there is provideda process for preparing an electrophotographic photosensitive memberwhich comprises:

(a) evacuating a pressure-reducible deposition chamber in which a targetcomposed of silicon and a substrate for electrophotography are disposedin fixed positions, to reduce the pressure,

(b) heating said substrate to 50°-350° C.,

(c) introducing a gas containing a hydrogen atom as a constituent atominto said deposition chamber,

(d) causing electric discharge in space of said deposition chamber inwhich said target is present, by electric energy to ionize said gas, and

(e) depositing amorphous silicon on said substrate at a deposition rateof 0.5-100 angstroms/sec. by utilizing said electric discharge whilecontinuing the electric discharge for a period of time sufficient toform an amorphous silicon photoconductive layer of a predeterminedthickness.

According to a further aspect of the present invention there is provideda process for preparing an electrophotographic photosensitive memberwhich comprises:

(a) evacuating a pressure-reducible deposition chamber in which asubstrate for electrophotography is disposed in a fixed position, toreduce the pressure in the deposition chamber,

(b) heating said substrate,

(c) introducing a rare gas, not less than 10% by volume of a silane gasbased on the rare gas, and a gas containing an element of Group IIIA orVA of the Periodic Table as a constituent atom into said depositionchamber, and causing electric discharge with an electric current densityof 0.1-10 mA/cm² and a voltage of 100-5000 V in space of said depositionchamber by electric energy to ionize said gases, and

(d) depositing amorphous silicon on said substrate at a deposition rateof 0.5-100 angstroms/sec. by utilizing said electric discharge whileraising the temperature of said substrate from the starting temperature(T₁), to form an amorphous silicon photoconductive layer.

According to a further aspect of the present invention there is provideda process for preparing an electrophotographic photosensitive memberwhich comprises:

(a) evacuating a pressure-reducible deposition chamber in which asubstrate for electrophotography is disposed in a fixed position, toreduce the pressure in the deposition chamber,

(b) heating said substrate,

(c) introducing a rare gas, not less than 10% by volume of a silane gasbased on the rare gas, and a gas containing an element of Group IIIA orVA of the Periodic Table as a constituent atom into said depositionchamber, and causing electric discharge with an electric current densityof 0.1-10 mA/cm² and a voltage of 100-5000 V in space of said depositionchamber by electric energy to ionize said gases,

(d) depositing amorphous silicon on said substrate at a deposition rateof 0.5-100 angstroms/sec. by utilizing said electric discharge to forman amorphous silicon photoconductive layer, and

(e) while forming said amorphous silicon layer, raising the temperatureof said substrate from the starting temperature (T₁) to a temperature(T₂) and then decreasing the temperature to a temperature lower than thetemperature (T₂).

According to a further aspect of the present invention there is provideda process for preparing an electrophotographic photosensitive memberwhich comprises:

(a) evacuating a pressure-reducible deposition chamber in which asubstrate for electrophotography is disposed in a fixed position, toreduce the pressure in the deposition chamber,

(b) heating said substrate,

(c) introducing a rare gas, not less than 10% by volume of a silane gasbased on the rare gas, and a gas containing an element of Group IIIA orVA of the Periodic Table as a constituent atom into said depositionchamber, and causing electric discharge with an electric power of0.1-300 W in space of said deposition chamber by electric energy toionize said gas mixture,

(d) depositing amorphous silicon on said substrate at a deposition rateof 0.5-100 angstroms/sec. by utilizing said electric discharge whileraising the temperature of said substrate from the starting temperature(T₁) to form an amorphous silicon photoconductive layer.

According to a further aspect of the present invention there is provideda process for preparing an electrophotographic photosensitive memberwhich comprises:

(a) evacuating a pressure-reducible deposition chamber in which asubstrate for electrophotography is disposed in a fixed position, toreduce the pressure in the deposition chamber,

(b) heating said substrate,

(c) introducing a rare gas, not less than 10% by volume of a silane gasbased on the rare gas, and a gas containing an element of Group III A ofor VA of the Periodic Table as a constituent atom into said depositionchamber, and causing electric discharge with an electric power of0.1-300 W in space of said deposition chamber by electric energy toionize said gas mixture,

(d) depositing amorphous silicon on said substrate at a deposition rateof 0.5-100 angstroms/sec. by utilizing said electric discharge to forman amorphous silicon photoconductive layer, and

(e) while forming said amorphous silicon layer, raising the temperatureof said substrate from the starting temperature (T₁) to a temperature(T₂) and the decreasing the temperature to a temperature lower than thetemperature (T₂).

According to a further process of the present invention there isprovided a process for preparing an electrophotographic photosensitivemember which comprises:

(a) evacuating a pressure-reducible deposition chamber in which asubstrate for electrophotography is disposed, to reduce the pressure inthe deposition chamber,

(b) heating said substrate to 50°-350° C.,

(c) introducing a rare gas, not less than 10% by volume of a silane gasbased on the rare gas, and a gas containing an element of Group IIIA orVA of the Periodic Table as a constituent atom into said depositionchamber, and causing electric discharge with an electric current densityof 0.1-10 mA/cm² and a voltage of 100-5000 V in space of said depositionchamber by electric energy to ionize said gas mixture, and

(d) depositing amorphous silicon on said substrate at a deposition rateof 0.5-100 angstroms/sec. by utilizing said electric discharge to forman amorphous silicon photoconductive layer.

According to a further aspect of the present invention there is provideda process for preparing an electrophotographic photosensitive memberwhich comprises:

(a) evacuating a pressure-reducible deposition chamber in which asubstrate for electrophotography is disposed, to reduce the pressure inthe deposition chamber,

(b) heating said substrate to 50°-350° C.,

(c) introducing a rare gas, not less than 10% by volume of a silane gasbased on the rare gas, and a gas containing an element of Group III A orVA of the Periodic Table as a constituent atom into said depositionchamber, and causing electric discharge with an electric power of0.1-300 W in space of said deposition chamber by electric energy toionize said gas mixture, and

(d) depositing amorphous silicon on said substrate at a deposition rateof 0.5-100 angstroms/sec. by utilizing said electric discharge to forman amorphous silicon photoconductive layer.

According to a further aspect of the present invention, there isprovided a process for preparing an electrophotographic photosensitivemember which comprises:

(a) evacuating a pressure-reducible deposition chamber in which asubstrate for electrophotography is disposed, to reduce the pressure inthe deposition chamber,

(b) heating said substrate to 50°-350° C.,

(c) introducing a rare gas and not less than 10% by volume of a silanegas based on the rare gas into said deposition chamber, and causingelectric discharge with an electric current density of 0.1-10 mA/cm² anda voltage of 100-5000 V in space of said deposition chamber by electricenergy to ionize said gases and

(d) depositing amorphous silicon on said substrate at a deposition rateof 0.5-100 angstroms/sec. by utilizing said electric discharge to forman amorphous silicon photoconductive layer.

According to a further aspect of the present invention, there isprovided a process for preparing an electrophotographic photosensitivemember which comprises:

(a) evacuating a pressure-reducible deposition chamber in which asubstrate for electrophotography is disposed, to reduce the pressure inthe deposition chamber,

(b) heating said substrate to 50°-350° C.,

(c) introducing a rare gas and not less than 10% by volume of a silanegas based on the rare gas into said deposition chamber, and causingelectric discharge with an electric power of 0.1-300 W in space of saiddeposition chamber by electric energy to ionize said gases, and

(d) depositing amorphous silicon on said substrate at a deposition rateof 0.5-100 angstroms/sec. by utilizing said electric discharge to forman amorphous silicon photoconductive layer.

According to a further aspect of the present invention, there isprovided a process for preparing an electrophotographic photosensitivemember which comprises:

(a) evacuating a pressure-reducible deposition chamber in which a targetcomposed of silicon and a substrate for electrophotography are disposedin fixed positions, to reduce the pressure

(b) heating said substrate to 50°-350° C.,

(c) introducing a gas containing a hydrogen atom as a constituent atom,a rare gas and a gas containing an element of Group IIIA or VA of thePeriodic Table as a constituent atom into said deposition chamber, andcausing electric discharge in space of said deposition chamber with anelectric current density of 0.1-10 mA/cm² and a voltage of 100-5000 V byelectric energy to ionize said gases, and

(d) depositing amorphous silicon on said substrate at a deposition rateof 0.5-100 angstroms/sec. by utilizing said electric discharge to forman amorphous silicon photoconductive layer.

According to a further aspect of the present invention, there isprovided an electrophotographic photosensitive member comprising asubstrate for electrophotography, a barrier layer capable of preventinginjection of electric carrier from said substrate side when the chargingtreatment is applied to said photosensitive member, and aphotoconductive layer overlying said barrier layer, said photoconductivelayer being formed of amorphous silicon by utilizing electric discharge,containing 10-40 atomic percent of hydrogen and being 5-80 microns inthickness.

According to a further aspect of the present invention, there isprovided an electrophotographic photosensitive member comprising asubstrate for electrophotography; a photoconductive layer, saidphotoconductive layer being formed of amorphous silicon by utilizingelectric discharge, containing 10-40 atomic percent of hydrogen andbeing 5-80 microns in thickness; and a covering layer overlying thesurface of said photoconductive layer, said covering layer being 0.5-70microns in thickness.

According to a further aspect of the present invention, there isprovided an electrophotographic photosensitive member comprising asubstrate for electrophotography and a photoconductive layer, saidphotoconductive layer being formed of amorphous silicon by utilizingelectric discharge, containing 10-40 atomic percent of hydrogen andbeing 5-80 microns in thickness.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 and FIG. 2 are schematic cross sectional views of embodiments ofelectrophotographic photosensitive members according to the presentinvention; and

FIG. 3, FIG. 4 and FIG. 5 are schematic diagrams of apparatuses suitablefor conducting the process for preparing an electrophotographicphotosensitive member according to the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT

FIG. 1 and FIG. 2 show representative structures of electrophotographicphotosensitive members according to the present invention.

Referring to FIG. 1, electrophotographic photosensitive member 1 iscomposed of substrate for electrophotography 2 and photoconductive layer3 mainly composed of amorphous silicon (hereinafter called a-Si), andthe photoconductive layer 3 has free surface 4 which becomes an imagebearing surface.

Substrate 2 may be electroconductive or electrically insulating. As aconductive substrate, there may be mentioned stainless steel, Al, Cr,Mo, Au, Ir, Nb, Ta, V, Ti, Pt, Pd and the like and alloys thereof. As anelectrically insulating substrate, synthetic resin films or sheets suchas polyesters, polyethylenes, polycarbonates, cellulose triacetate,polypropylene, polyvinyl chloride, polyvinylidene chloride, polystyrenepolyamides and the like glass, ceramics, paper and the like. At leastone surface of these electrically insulating substrates is preferablyconductivized.

For example, in case of glass, its surface is conductivized with In₂ O₃,SnO₂ or like. In case of synthetic resin film such as polyester film andthe like, its surface is conductivized with Al, Ag, Pb, Zn, Ni, Au, Cr,Mo, Ir, Nb, Ta, V, Ti, Pt and the like by vapor deposition, electronbeam vapor deposition, sputtering and the like, or by laminating thesurface with such metal.

As a shape of the substrate, there may be used drum, belt, plate andother optional shapes. In case of a continuous high copying, an endlessbelt or drum shape is preferable.

The thickness of the substrate is optional. When a flexibleelectrophotographic photosensitive member is desired, a thickness asthin as possible is preferable, but it is usually not less than 10microns from manufacturing, handling and mechanical strength points ofview.

a-Si photoconductive layer 3 is prepared on substrate 2 with siliconand/or silane and the like silicon compound by glow discharge,sputtering, ion plating, ion implantation, and the like. Thesemanufacturing methods may be optionally selected depending uponmanufacturing conditions, capital investment, manufacture scales,electrophotographic properties and the like. Glow discharge ispreferably used because controlling for obtaining desirableelectrophotographic properties is relatively easy and impurities ofGroup III or Group V of the Periodic Table can be introduced into thea-Si layer in a substitutional type for the purpose of controlling thecharacteristics.

Further, according to the present invention, glow discharge andsputtering in combination can be conducted in the same system to forma-Si layer and this is a very efficient and effective method.

a-Si photoconductive layer 3 is controlled by incorporating H (hydrogen)(as the result, H is contained in a-Si layer) so as to obtain desirabledark electrical resistive and photoconductive gain suitable forphotoconductive layers of electrophotographic photosensitive members.

In the present invention, "H is contained in a-Si layer" means one of ora combination of the state, i.e. "H is bonded to Si", and ionized H isweakly bonded to Si in the layer" and "present in the layer in a form ofH₂ ".

In order to incorporate H in a-Si photoconductive layer 3 resulting inthat H is contained in a-Si layer, a silicon compound such as silanes,for example, SiH₄, Si₂ H₆, and the like or H₂ may be introduced to anapparatus for producing a photoconductive layer 3 upon producing thephotoconductive layer 3, and then heat-decomposed or subjected to glowdischarge to decompose the compound or H₂ and incorporate H in the a-Silayer as the layer grows, or H may be incorporate in the a-Si layer byion implantation.

According to the present inventor's opinion, content of H in an a-Siphotoconductive layer 3 is a very important factor affecting whether thea-Si photoconductive layer is suitable for electrography.

As a photoconductive layer for electrophotographic photosensitivemembers, amount of H in an a-Si layer is usually 10-40 atomic %,preferably, 15-30 atomic %.

Any theoretical reason why content of H in a-Si layer is to be theabove-mentioned range is not yet clear, but when the content of H isoutside of the above range, a photoconductive layer made of such a-Si ofan electrophotographic photosensitive member has a low dark resistancewhich is not suitable for the photoconductive layer and thephotosensitivity is very low or is hardly observed, and further increasein carrier caused by light irradiation is very little.

For the purpose of incorporating H in a-Si layer (i.e. causing a statethat H is contained in a-Si layer), when glow discharge is employed, asilicon hydride gas such as SiH₄, Si₂ H₆ and the like may be used as thestarting material for forming the a-Si layer, and therefore, H isautomatically incorporated in the a-Si layer upon formation of the a-Silayer by decomposition of such silicon hydride. In order to carry outthis incorporation of H more efficiently, H₂ gas may be introduced intothe system where glow discharge is carrie out to form a-Si layer.

Where sputtering is employed, in a rare gas such as Ar or a gas mixtureatmosphere containing a rare gas sputtering is carried out with Si as atarget while introducing H₂ gas into the system or introducing siliconhydride gas such as SiH₄, Si₂ H₆ and the like or introducing B₂ H₆, PH₃or the like gas which can serve to doping with impurities.

Controlling an amount of H to be contained in a-Si layer can be effectedby controlling the substrate temperature and/or an amount introducedinto the system of a starting material used for incorporating H.

a-Si layer can be made intrinsic by appropriately doping with impuritieswhen prepared and the type of conductivity can be controlled. Therefore,polarity of charging upon forming electrostatic images on anelectrophotographic photosensitive member thus prepared can beoptionally selected, that is, positive or negative polarity can beoptionally selected.

In case of conventional Se photoconductive layer, only p-type or at mostintrinsic type (i-type) of photoconductive layer can be obtained bycontrolling the substrate temperature, type of impurities, amount ofdopant and other preparation conditions, and moreover, even when thep-type is prepared, the substrate temperature should be strictlycontrolled. In view of the foregoing, the a-Si layer is much better andmore convenient than conventional Se photoconductive layers.

As an impurity used for doping a-Si layer to make the a-Si layer p-typethere may be mentioned elements of Group III A of the Periodic Tablesuch as B, Al, Ga, In, Tl and the like, and as an impurity for dopinga-Si layer to make the a-Si layer n-type, there may be mentionedelements of Group VA of the Periodic Table such as N, P, As, Sb, Bi andthe like.

These impurities are contained in the a-Si layer in an order of ppm. sothat problem of pollution is not so serious as that for a main componentof a photoconductive layer. However, it is naturally preferable to payattention to such problem of pollution. From this viewpoint, B, As, Pand Sb are the most appropriate taking into consideration electrical andoptical characteristics of a-Si photoconductive layers to be produced.

An amount of impurity with which a-Si layers are doped may beappropriately selected depending upon electrical and opticalcharacteristics of the a-Si photoconductive layer. In case of impuritiesof Group IIIA of the Periodic Table, the amount is usually 10⁻⁶ -10⁻³atomic %, preferably, 10⁻⁵ -10⁻⁴ atomic %, and in case of impurities ofGroup VA of the Periodic Table, the amount is usually 10⁻⁸ -10⁻⁵ atomic%, preferably 10⁻⁸ -10⁻⁷ atomic %.

The a-Si layers may be doped with these impurities by various methodsdepending upon the type of method for preparing the a-Si layer. Thesewill be mentioned later in detail.

Referring to FIG. 1, electrophotographic photosensitive member 1contains a-Si photoconductive layer 3 which has a free surface 4. Incase of an electrophotographic photosensitive member to the surface ofwhich charging is applied for the purpose of forming electrostaticimages, it is preferable to dispose between a-Si photoconductive layer 3and substrate 2 a barrier layer capable of suppressing injection ofcarriers from the side of substrate 2 upon charging for producingelectrostatic images.

As a material for such barrier layer, there may be selected insulatinginorganic oxides such as Al₂ O₃, SiO, SiO₂ and the like and insulatingorganic compounds such as polyethylene, polycarbonate, polyurethane,polyparaxylylene and the like, Au, Ir, Pt, Rh, Pd, Mo and the like.

Thickness of the a-Si photoconductive layer is selected taking intoconsideration its electrostatic characteristic, using conditions, forexample, whether flexibility is required. It is usually 5-80 microns,preferably, 10-70 microns, and more preferably, 10-50 microns.

As shown in FIG. 1, the a-Si photoconductive layer surface is directlyexposed and refractive index (n) of a-Si layer is as high as about3.3-3.9 and therefore, light reflection at the surface is apt to occurupon exposure as compared with conventional photoconductive layers, andlight amount absorbed in a photoconductive layer is lowered resulting inincrease in loss of light. In order to reduce the loss of light, it ishelpful to dispose an antireflection layer on an a-Si photoconductivelayer.

Materials for the antireflection layer are selected taking the followingconditions into consideration.

i) No adverse effect on the a-Si photoconductive layer;

ii) High antireflecting property; and

iii) Electrophotographic characteristics such as electric resistancehigher than a certain value, transparent to a light absorbed to thephotoconductive layer, good solvent resistance when used for a liquiddeveloping process, causing no deterioration of the already prepareda-Si photoconductive layer upon preparing the antireflection layer, andthe like.

Further, for the purpose of facilitating antireflection, it is desirableto select refractive index of the material which is between that of thea-Si layer and that of air. This will be clear from a simple calculationof optics.

Thickness of the antireflection layer is preferably λ/4√n where n isrefractive index of the a-Si layer and λ is wavelength of exposurelight, or (2k+1) times of λ/4√n where k is an integer such as 0,1, 2, 3,. . . , most preferably λ/4√n taking into consideration of lightabsorption of the antireflection layer itself.

Taking these optical conditions, thickness of the antireflection layeris preferably 50-100 mμ assuming that wavelength of the exposure lightis roughly in the wavelength region of visible light.

Representative materials for an antireflection layer are inorganicfluorides and oxides such as MgF₂, Al₂ O₃, ZrO₂, TiO₂, ZnS, CeO₂, CeF₂,SiO₂, SiO, Ta₂ O₅, AlF₃.3NaF and the like, and organic compounds such aspolyvinyl chloride, polyamide resins, polyimide resins, polyvinylidenefluoride, melamine resins, epoxy resins, phenolic resins, celluloseacetate and the like.

The surface of a-Si photoconductive layer 3 may be provided with asurface coating layer such as a protective layer, an electricallyinsulating layer and the like as in conventional electrophotographicphotosensitive members. FIG. 2 shows such electrophotographicphotosensitive member having a covering layer.

Now referring to FIG. 2, electrophotographic photosensitive member 5 hascovering layer 8 on a-Si photoconductive layer 7 overlying substrate,but other structure is the same as that of FIG. 1.

Characteristics required of covering layer 8 vary depending upon eachelectrophotographic process. For example, when an electrophotographicprocess such as U.S. Pat. Nos. 3,666,363 and 3,734,609 is used, it isrequired that covering layer 8 is electrically insulating and has asufficient electrostatic charge retaining property when subjected tocharging and a thickness thicker than a certain thickness. However, whena Carlson type electrophotographic process is used, a very thin coveringlayer 8 is required since potentials at the light portions ofelectrostatic images are preferably very low. Covering layer 8 is to beprepared so as to satisfy the desired electrical characteristics andfurthermore, the following are taken into consideration not adverselyaffecting a-Si photoconductive layers chemically and physically,electrical contact and adhesivity with a-Si photoconductive layer,moisture resistance, abrasion resistance and cleaning properties.

Representative materials for a covering layer are synthetic resins suchas polyethylene terephthalate, polycarbonate, polypropylene, polyvinylchloride, polyvinylidene chloride, polyvinyl alcohol, polystyrene,polyamides, polyethylene tetrafluoride, polyethylene trifluoridechloride, polyvinyl fluoride, polyvinylidene fluoride, copolymers ofpropylene hexafluoride and ethylene tetrafluoride, copolymers ofethylene trifluoride and vinylidene fluoride, polybutene, polyvinylbutyral, polyurethane and the like, and cellulose derivatives such asthe diacetate, triacetate and the like.

These synthetic resin and cellulose derivative in a form of film may beadhered to the surface of the a-Si photoconductive layer, or a coatingliquid of these materials is coated on an a-Si photoconductive layer 7.Thickness of the covering layer may be appropriately selected depend-inupon the required characteristics and type of material, but it isusually 0.5-70 microns. When the covering layer is used as a protectivelayer, the thickness is usually, for example not more than 10 micronsand when it is used as an electrically insulating layer, the thicknessis usually, for example, not less than 10 microns though this value, 10microns is not critical, but only an example because such value variesdepending upon type of the material, the electrophotographic process andstructure of the electrophotographic photosensitive member.

The covering layer 8 may also serve as an antireflection layer and thusthe function is effectively widened.

Preparation of electrophotographic photosensitive member of the presentinvention is exemplified by a glow discharge process and a sputteringprocess below.

Referring to FIG. 3, there is illustrated a diagrammatical glowdischarge process of capacitance type for producing anelectrophotographic photosensitive member.

Glow discharge deposition chamber 10 contains substrate 11 fixed tofixing member 12 and an a-Si photoconductive layer is formed onsubstrate 11. Under substrate 11 is disposed heater 13 for heatingsubstrate 11. At upper part of deposition chamber 10 are woundcapacitance type electrodes 15 and 15' connected to high frequency powersource 14. When the power source 14 is turned on, a high frequencyvoltage is applied to electrodes 15 and 15' to cause glow discharge indeposition chamber 10.

To the top portion of deposition chamber 10 is connected a gasintroducing conduit to introduce gases from gas pressure vessels 16, 17and 18 into deposition chamber 10 when required.

Flow meters 19, 20 and 21, flow rate controlling valves 22, 23 and 24,valves 25,26 and 27 and auxiliary valve 28 are provided

The lower portion of deposition chamber 10 is connected to an exhaustingdevice (not shown) through main valve 29. Valve 30 serves to breakvacuum in deposition chamber 10.

Cleaned substrate 11 is fixed to fixing member 12 with the cleanedsurface kept upward.

Surface of substrate 11 may be cleaned as shown below. It can be cleanedwith an alkali or acid, (a kind of chemical treatment), or by disposinga substrate cleaned to some extent in deposition chamber 11 at a fixedportion and then applying glow discharge. In the latter case, cleaningsubstrate 11 and formation of an a-Si photoconductive layer can becarried out in the same system without breaking vacuum and thereby itcan be avoided that dirty matters and impurities attach to the cleanedsurface. After fixing substrate 11 to fixing member 12, main valve 29 isfully opened to evacuate deposition chamber 10 to bring the pressuredown to about 10⁻⁵ Torr. Then heater 13 starts to heat substrate 11 upto a predetermined temperature, and the temperature is kept whileauxiliary valve 28 is fully opened, and then valve 25 of gas pressurevessel 16 and valve 26 of gas pressure vessel 17 are fully opened. Gaspressure vessel 16 is, for example, for a diluting gas such as Ar andgas pressure vessel 17 is for a gas forming a-Si, for example, siliconhydride gas such as SiH₄, Si₂ H₆, Si₄ H₁₀ or their mixture. Pressurevessel 18 may be used, if desired, for storing a gas capable ofincorporating impurities in an a-Si photoconductive layer, for example,PH₃, P₂ H₄, B₂ H₆ and the like. Flow rate controlling valves 22 and 23are gradually opened while observing flow meters 19 and 20 to introducea diluent gas, e.g., Ar, and a gas for forming a-Si, e.g., SiH₄ intodeposition chamber 10. The diluting gas is not always necessary, butonly SiH₄ may be introduced into the system. When Ar gas is mixed with agas for forming a-Si, e.g. SiH₄, and then introduced, the amount ratiomay be determined depending upon each particular situation. Usually thegas for forming a-Si is more than 10 vol.% based on the diluting gas. Asthe diluting gas, a rare gas such as He may be used. When gases areintroduced from pressure vessels 16 and 17 into deposition chamber 10,main valve 29 is adjusted to keep a particular vacuum degree, usually,an a-Si layer forming gas of 10⁻¹² -3 Torr. Then, to electrodes 15 and15' is applied a high frequency voltage, for example, 0.2-30 MHz, fromhigh frequency power source 14 to cause glow discharge in depositionchamber 10, and SiH₄ is decomposed to deposit Si on substrate 11 to forman a-Si layer.

Impurities may be introduced into an a-Si photoconductive layer to beformed by introducing a gas from pressure vessel 18 into depositionchamber 10 upon forming an a-Si photoconductive layer. By controllingvalve 24, an amount of gas introduced into deposition chamber 10 frompressure vessel 18 can be controlled. Therefore, an amount of impuritiesincorporated in an a-Si photoconductive layer can be optionallycontrolled and in addition, the amount may be varied in the direction ofthickness of the a-Si photoconductive layer.

In FIG. 3, the glow discharge deposition apparatus uses a glow dischargeprocess of RF (radio frequency) capacitance type, but in place of saidtype process, there may be used a glow dischage process of RF inductancetype or DC diode type. Electrodes for glow discharge may be disposed inor outside of deposition chamber 10.

In order to efficiently carry out glow discharge in a glow dischargeapparatus of capacitance type as shown in FIG. 3, current density isusually 0.1-10 mA/cm², preferably 0.1-5 mA/cm², more preferably, 1-5mA/cm², of AC or DC, and further the voltage is usually 100-5000 V,preferably 300-5000 V, so as to obtain a sufficient power.

Characteristics of an a-Si photoconductive layer depend on a temperatureof substrate to a great extent and therefore, it is preferable tocontrol the temperature strictly. The temperature of substrate accordingto the present invention is usually 50°-350° C., preferably 100°-200° C.so as to obtain an a-Si photoconductive layer for electrophotographyhaving desirable characteristics. In addition, the substrate temperaturemay be changed continuously or batchwise to produce desirablecharacteristics. Growing speed of the a-Si layer also affects physicalproperties of the resulting a-Si layer to a great extent, and accordingto the present invention it is usually 0.5-100 Å/sec., preferably 1-50Å/sec.

FIG. 4 shows a diagrammatical apparatus for producingelectrophotographic photosensitive members by sputtering.

Deposition chamber 31 contains substrate 32 fixed to fixing member 33which is conductive and is electrically insulated from depositionchamber 31. Heater 34 is disposed under substrate 32, which is to beheated by heater 34. Over substrate 32 and facing substrate 32, there isdisposed polycrystal or single crystal silicon target 35. High frequencyvoltage is applied between fixing member 33 and silicon target 35 byhigh frequency power source 36.

To deposition chamber 31 are connected gas pressure vessels 37 and 38through valves 39 and 40, flow meters 41 and 42, flow rate controllingvalves 43 and 44, and auxiliary valve 45. Gases may be introduced intodeposition chamber 30 when wanted.

An a-Si photoconductive layer can be formed on substrate 32 by theapparatus of FIG. 4 as shown below. Deposition chamber 31 is evacuatedto the direction of arrow B to obtain an appropriate degree of vacuum.Then substrate 32 is heated to a particular temperature by heater 34.

When sputtering is employed, the temperature of substrate 32 is usually50°-350° C., preferably, 100°-200° C. This substrate temperature affectsgrowing speed of the a-Si layer, structure of the layer, void, physicalproperties of the resulting a-Si layer, and therefore, a strict controlis necessary.

The substrate temperature may be kept constant during formation of ana-Si layer, or may be raised or lowered or both raised and lowered incombination as the a-Si layer grows. For example, at the beginning offormation of an a-Si layer a substrate temperature is kept at arelatively low temperature T₁ and when the a-Si layer grows to someextent, the substrate temperature is raised up to T₂ (T₂ >T₁) duringforming the a-Si layer, and then at the end of the a-Si layer formationthe substrate temperature is lowered down to a temperature T₃ lower thanT₂. In this way, electrical and optical properties of the a-Siphotoconductive layer can be constantly or continuously changed in thedirection of thickness of the layer.

Since the layer growing speed of a-Si is slower than, for example, Se,there is a fear that the a-Si formed at the beginning (a-Si near thesubstrate) may change its original characteristics before the layerformation is completed where the layer is thick. Therefore, it ispreferable to form the layer by raising the substrate temperature fromthe beginning to the end so as to obtain an a-Si layer having uniformcharacteristic in the direction of thickness.

The substrate temperature controlling method may also be employed whenglow discharge process is carried out.

After detecting that the temperature of substrate 32 is heated to apredetermined temperature, auxiliary valve 45, valves 39 and 40 arefully opened and then while main valve 46 and flow rate controlling 44are controlled, silicon hydride gas such as SiH₄ and the like and/orhydrogen gas are introduced from pressure vessel 38 into depositionchamber 31 resulting in decrease in degree of vacuum and then theresulting degree of vacuum is kept.

Then, flow rate controlling valve 43 is opened and an atmosphere gassuch as Ar gas is introduced from pressure vessel 37 into depositionchamber 31 until the degree of vacuum decreases The flow rates ofsilicon hydride gas, hydrogen gas, and the atmosphere gas such as Ar areappropriately determined so as to obtain desired physical properties ofthe a-Si photoconductive layer. For example, pressure of a mixture of anatmosphere gas and hydrogen gas in deposition chamber is usually 10⁻³-10⁻¹ Torr preferably 5×10⁻³ -3×10⁻². In place of Ar gas, there may beused other rare gases such as He gas.

After an atmosphere gas such as Ar and the like, and H₂ gas or siliconhydride gas are introduced into deposition chamber 31, a high frequencyvoltage is applied between substrate 32 is applied between fixing member33 and silicon target 35 from a high frequency power source 36 at apredetermined frequency and voltage to discharge and the resultingatmosphere gas ion such as Ar ion serves to sputter silicon of thesilicon target to form an a-Si layer on substrate 32.

FIG. 4 is explained concerning sputtering by a high frequency dischargebut there may be used there sputtering by DC discharge. In case ofsputtering by high frequency discharge, the frequency is usually 0.2-30MHz preferably 5-20 MHz, and the current density of discharge is usually0.1-10 mA/cm², preferably 0.1-5 mA/cm², more preferably 1-5 mA/cm². Inaddition, for the purpose of obtaining sufficient power, the voltage isusually controlled to 100-5000 V, preferably 300-5000 V.

A growing speed of an a-Si layer by sputtering is mainly determined bythe substrate temperature and discharging conditions, and affectsphysical properties of the resulting a-Si layer to a great extent. Agrowing speed of an a-Si layer for attaining the purpose of the presentinvention is usually 0.5-100 Å/sec., preferably 1-50 Å/sec. In asputtering method as well as a glow discharge method, it is possible tocontrol the resulting a-Si photoconductive layer to n-type or p-type bydoping with impurities. Introduction of impurities in a sputteringmethod is similar to that in a glow discharge method. For example, amaterial such as PH₃, P₂ H₄, B₂ H₆ and the like is introduced intodeposition chamber in a gaseous form upon producing an a-Si layer andthe a-Si layer is doped with P or B as an impurity. Further, impuritiescan be introduced into an already produced a-Si layer by an ionimplantation method and it is possible to control the very thin surfacelayer of the a-Si layer to a particular conductive type.

FIG. 5 illustrates diagrammatically a glow discharge depositionapparatus for producing an electrophotographic photosensitive member byinductance type glow discharge.

Glow discharge deposition chamber 47 contains substrate 48 on which ana-Si photoconductive layer is formed. Substrate 48 is fixed to fixingmember 49. Under substrate 48 is disposed heater 50 to heat substrate48. Inductance type electrode 52 connected to a high frequency powersource 51 is wound around the upper portion of deposition chamber 47.When the power source is on, high frequency wave is applied to theelectrode 52 to cause glow discharge in deposition chamber 47. To thetop of deposition chamber 47 is connected a gas introducing pipe capableof introducing gases in gas pressure vessels 53, 54 and 55 whenrequired. The gas introducing pipe is equipped with flow meters 56, 57and 58, flow rate controlling valves 59, 60 and 61, valves 62, 63 and 64and auxiliary valve 65.

The bottom portion of deposition chamber 47 is connected to anexhausting device (not shown) through main valve 66. Valve 66 is usedfor breaking vacuum in deposition chamber 47. Gases from pressurevessels 53, 54 and 55 are not directly introduced into depositionchamber 47, but are mixed in advance in this mixing tank 68 and then theresulting mixture gas is introduced into deposition chamber 47. In thisway, when the gases are once introduced into mixing tank 68 and mixed ata predetermined ratio and then the resulting mixture is introduced intodeposition chamber 47 from mixing tank 68 it is possible to introducealways a gas mixture of a constant mixing ratio into deposition chamber47 at any time. This is very advantageous.

An a-Si photoconductive layer having a desired characteristics is formedon substrate 48 as shown below.

Cleaned substrate 48 is fixed to fixing member 49 with the cleanedsurface upward. Cleaning the surface of substrate 48 is conducted as inFIG. 3.

Deposition chamber 47 and mixing tank 68 are evacuated while main valve66 and auxiliary valve 65 are kept fully open. The pressure in thesystem is brought down to about 10⁻⁵ Torr., and then substrate 48 isheated to a predetermined temperature by heater 50 and the temperatureis kept.

Then auxiliary valve is closed and valves 62 and 63 are fully opened.Gas pressure vessel 53 contains a diluting gas such as Ar gas, gaspressure vessel 54 contains a gas for forming a-Si such as siliconhydride gas, for example, SiH₄, Si₂ H₆, Si₄ H₁₀ and mixture thereof, andgas pressure vessel 55 contains a gas for forming impurities to beintroduced into the a-Si photoconductive layer, if desired, such as PH₃,P₂ H₄, B₂ H₆ and the like.

Flow rate controlling valves 59 and 60 are gradually opened whilewatching flow meters 56 and 57 and thus gases in pressure vessels 53 and54 are fed to mixing tank 68 at a desired ratio in a desired amount toform a gas mixture, for example, a mixture of Ar and SiH₄. Then flowrate controlling valves 59 and 60 are closed and auxiliary valve 65 isgradually opened to introduce the gas mixture into deposition chamber 47from mixing tank 68. In this case, a diluting gas such as Ar is notalways necessary and it is allowed to introduce only a gas for forminga-Si such as SiH₄ and the like.

The ratio of a diluting gas to a gas for forming a-Si introduced intomixing tank 68 may be optionally selected as wanted. The ratio isusually more than 10 vol. % of a gas for forming a-Si based on adiluting gas. As the diluting gas, He gas may be used in place of Argas. Deposition chamber 47 is maintained at a desired pressure, forexample 10⁻² -3 Torr. by controlling main valve 66. Then, to electrodeof induction type 52 wound around deposition chamber 47 is applied apredetermined high frequency voltage, for example, 0.2-30 MHz, by highfrequency power source 51 to cause glow discharge in deposition chamber47 and decompose SiH₄ gas and Si is deposited on substrate 48 to form ana-Si layer.

If it is desired to introduce impurities into an a-Si photoconductivelayer, the gas in pressure vessel 55 is introduced into mixing tank 68together with the other gases. An amount of the gas forimpurity-introducing can be controlled by flow rate controlling-valve 61so that the amount of impurities introduced into the a-Siphotoconductive layer can be optionally controlled.

In a glow discharge apparatus of inductance type as in FIG. 5, the highfrequency power for producing an a-Si layer having desiredcharacteristics may be determined accordingly, but it is usually 0.1-300W, preferably 0.1-150 W, more preferably 5-50 W. And characteristics ofthe resulting a-Si photoconductive layer is affected by the substratetemperature upon growing the a-Si layer and the growing speed of thelayer to a great extent. Therefore, these factors should be strictlycontrolled. Desirable conditions of substrate temperature and growingspeed of a-Si layer in a glow discharge apparatus of inductance type aresimilar to those mentioned concerning FIG. 3.

The invention will be understood more readily by reference to thefollowing examples; however, these examples are intended to illustratethe invention and are not to be construed to limit the scope of theinvention.

EXAMPLE 1

In accordance with the procedure described below, an electrophotographicphotosensitive member of the present invention was prepared by using anapparatus as shown in FIG. 3, and image forming treatment was applied tothe photosensitive member.

An aluminum substrate was cleaned in such a manner that the surface ofthe substrate was treated with a 1% solution of NaOH and sufficientlywashed with water and then dried. This substrate, which was 1 mm inthickness and 10 cm×5 cm in size, was firmly disposed at a fixedposition in a fixing member 12 placed at a predetermined position in adeposition chamber 10 for glow discharge so that the substrate was keptapart from a heater 13 equipped to the fixing member 12 by about 1.0 cm.

The air in the deposition chamber 10 was evacuated by opening fully amain valve 29 to bring the chamber to a vacuum degree of about 5×10⁻⁵Torr. This is illustrated by label A↓ in FIG. 3. The heater 13 was thenignited to heat uniformly the aluminum substrate to 150° C., and thesubstrate was kept at this temperature a subsidiary valve 28 was fullyopened, and subsequently a valve 25 of a bomb 16 to which Ar was chargedand a valve 26 of a bomb 17 which was filled with SiH₄ were also openedfully, and thereafter, flow amount controlling valves 22, 23 weregradually opened so that Ar gas and SiH₄ gas were introduced into thedeposition chamber 10 from the bombs 16, 17. At that time, the vacuumdegree in the deposition chamber 10 was brought to and kept at about0.075 Torr. by regulating the main valve 29.

A high frequency power source 14 was switched on to apply a highfrequency voltage of 13.56 MHz between electrodes 15 and 15' so that aglow discharge was caused, thereby depositing and forming an a-Si typephotoconductive layer on the aluminum substrate. At that time, the glowdischarge was initiated with an electric current density of about 0.5mA/cm² and a voltage of 500 V. Further, the growth rate of the a-Silayer was about 4 angstroms per second and the deposition was effectedfor 15 hours and further the thus formed a-Si layer had a thickness of20 microns.

After completion of the deposition, while the main valve 29, valves 25and 26, flow amount controlling valves 22 and 23, and subsidiary valve28 were closed, a valve 30 was opened to break the vacuum state in thedeposition chamber 10. The prepared photosensitive member was taken outfrom the apparatus.

To the a-Si type photoconductive layer surface of the photosensitivemember was applied negative corona discharge with a power source voltageof 5500 V in a dark place. The image exposure was conducted in anexposure quantity of 15 lux·sec. to form an electrostatic image, whichwas then developed with a positively charged toner in accordance withthe cascade method. The developed image was transferred to a transferpaper and then fixed so that an extremely sharp image with a highresolution was obtained.

The image forming process as mentioned above was repeatedly carried outin order to test the durability of the photosensitive member. As aresult, the image on a transfer paper obtained when such process wasrepeated ten thousand (10,000) times was extremely good in the quality.Although such image was compared with the first image on a transferpaper obtained at the time of the initial operation of the image formingprocess, no different was observed therebetween. Therefore, it was foundthat the photosensitive member is excellent in the corner dischargingresistance, abrasion resistance, cleaning property and the like andshows extremely excellent durability. In addition, the blade cleaningwas effected in cleaning the photosensitive member after thetransferring step, a blade formed of urethane rubber was used.

Further, the foregoing image forming process was repeated under the samecondition except that positive corona discharge was applied with avoltage of 6,000 V to the photosensitive member and a negatively chargedtoner was used for the developing. The thus obtained image formed on atransfer paper had an image density lower than that of the imageobtained in the foregoing image forming process using negative coronadischarge. As a result, it was recognized that the photosensitive memberprepared in this example depends upon the polarity to be charged.

EXAMPLE 2

In accordance with the procedure and condition used in Example 1, ana-Si type layer of 20 microns in thickness was formed on the aluminumsubstrate. The structure was taken out from the deposition chamber 10,and polycarbonate region was then coated onto the a-Si type layer toform an electrically insulating layer having a thickness of 15 micronsafter drying.

To the insulating layer surface of the electrophotographicphotosensitive member obtained in the above-mentioned manner was appliedpositive corona discharge with a power source voltage of 6,000 V as theprimary charging for 0.2 sec. so that such surface was charged to avoltage of +2,000 V. Next, negative corona discharging with a voltage of5,500 V was carried out as the secondary charging simultaneously withimage exposure in an exposure quantity of 15 lux·sec., and the wholesurface of the photosensitive member was then exposed uniformly to forman electrostatic image. This image was developed with a negativelycharged toner by the cascade method, and the thus developed image wastransferred to a transfer paper and fixed so that an image of extremelyexcellent quality was obtained.

EXAMPLE 3

In the following manner similar to that in Example 1, anelectrophotographic photosensitive member was prepared by using theapparatus as illustrated in FIG. 3 and the image forming treatment wasapplied to the photosensitive member.

An aluminum substrate having a thickness of 1 mm and a size of 10 cm×10cm was first treated with a 1% solution of NaOH and sufficiently washedwith water and dried to clean the surface of the substrate. Thissubstrate was firmly disposed at a fixed position in a fixing member 12placed at a predetermined position in a deposition chamber 10 for glowdischarge so that it might be kept apart from a heater 13 positioned inthe fixing member 12 by about 1.0 cm.

A main valve 29 was fully opened to evacuate the air in the depositionchamber 10 so that the vacuum degree in the chamber was adjusted toabout 5×10⁻⁵ Torr. The heater 13 was then ignited to heat uniformly thealuminum substrate to 150° C., the substrate being kept at thattemperature. Then, a subsidiary valve 28 was first opened fully, andsuccessively a valve 25 of a bomb 16 containing Ar charged thereto and avalve 26 of a bomb 17 containing SiH₄ charged. thereto were fullyopened. Thereafter, the flow amount controlling valves 22 and 23 weregradually opened so that Ar gas and SiH₄ gas were introduced into thedeposition chamber 10 from the bombs 16 and 17, respectively. At thistime, the vacuum degree in the deposition chamber 10 was kept at about0.075 Torr. by regulating the main valve 29, and while flow meters 19and 20 were carefully observed, the flow amount controlling valves 22and 23 were regulated to control the flow amount of the gases so thatthe flow amount of the SiH₄ gas might be 10% by volume based on that ofthe Ar gas.

A valve 27 of a bomb 18 containing B₂ H₆ charged thereto was fullyopened and a flow amount controlling valve 24 was slowly opened tointroduce B₂ H₆ gas into the deposition chamber 10 while the flow amountof the gas was controlled so that it might be 5×10⁻³ % by volume basedon the flow amount of the SiH₄ gas. In this case, the main valve 29 wasregulated to retain the vacuum degree in the deposition chamber 10 to0.075 Torr.

Subsequently, a high frequency power source 14 was switched on in orderto apply a high frequency voltage of 13.56 MHz between electrodes 15 and15' to give rise to the glow discharge so that an a-Si typephotoconductive layer is formed on the aluminum substrate by thedeposition. At the time of the glow discharge, the current density wasabout 3 mA/cm² and the voltage 500 V. Further, the growth rate of thea-Si type layer has about 4 angstroms/sec., the period of time for thedeposition 15 hours, and the thickness of the a-Si type layer 20microns. After completion of the deposition, the main valve 29,subsidiary valve 28, flow amount controlling valves 22, 23, 24, andvalves 25, 26, 27 were closed, but the valve 30 was opened to break thevacuum state in the deposition chamber 10. Then, the electrophotographicphotosensitive member obtained in the above mentioned manner was takenout from the apparatus.

To the a-Si type photoconductive layer surface of the photosensitivemember was applied negative corona discharge with a voltage of 5,500 Vin a dark place. The image exposure was conducted in an exposurequantity of 20 lux·sec. to form an electrostatic image, which was thendeveloped with a positively charged toner in accordance with the cascademethod. The developed image was transferred to a transfer paper and thenfixed so that an excellent sharp image was obtained.

The image forming process as mentioned above was repeatedly carried outin order to test the durability of the photosensitive member. As aresult, the image on a transfer paper obtained when such process wasrepeated ten thousand (10,000) times was extremely good in the quality.Although such image was compared with the first image on a transferpaper obtained at the time of the initial operation of the image formingprocess, no different was observed therebetween. Therefore, it was foundthat the photosensitive member is excellent in the durability. Inaddition, the blade cleaning was effected in cleaning the photosensitivemember after the transferring step, the blade being formed of urethanerubber.

Further, positive corona discharge with a power source voltage of 6,000V was applied to the photosensitive member in a dark place and the imageexposure was conducted in an exposure amount of 20 lux·sec. to form anelectrostatic image. This electrostatic image was developed with anegatively charged toner by the cascade method. The developed image wasthen transferred to a transfer paper and fixed so that an image withextreme sharpness was obtained.

It was found from this result and the before-mentioned result that thephotosensitive member obtained in this example does not havedependability to the charged polarity, but possesses properties of aphotosensitive member which produces advantageously good image wheneither polarity is charged.

EXAMPLE 4

The same procedure as in Example 3 was repeated except that the flowamount of the B₂ H₆ gas was adjusted to 5×10⁻⁴ % by volume based on theflow amount of the SiH₄ gas, to prepare an electrophotographicphotosensitive member having an a-Si type photoconductive layer of 20microns in thickness on the aluminum substrate.

In accordance with the same condition and manner as in Example 3, theimage forming process was carried out by using the obtainedphotosensitive member to form an image on a transfer paper. As a result,the image formed by the process using position corona discharge wasexcellent in quality and very sharp as compared with that obtained bythe process employing negative corona discharge.

It is recognized from the result that the photosensitive member of thisexample depends upon the polarity to be charged. In addition, thispolarity dependability is contrary to that of the photosensitive memberobtained in Example 1.

EXAMPLE 5

In accordance with the procedure and condition used in Example 4, ana-Si type layer of 20 microns in thickness was formed on the aluminumsubstrate. The structure was then taken. out from the deposition chamber10 to the outside, and polycarbonate resin was then coated onto the a-Sitype layer to form an electrically insulating layer having a thicknessof 15 microns after drying.

To the insulating layer surface of the electrophotographicphotosensitive member obtained in the above-mentioned manner was appliednegative corona discharge with a power source voltage of 6,000 V as theprimary charging for 0.2 sec. so that such surface was charged to avoltage of -2,000 V. Positive corona discharging with a voltage of 5,500V was carried out as the secondary charging simultaneously with theimage exposure in an exposure quantity of 15 lux·sec., and the wholesurface of the photosensitive member was then exposed uniformly to forman electrostatic image. This image was developed with a positivelycharged toner by the cascade method, and the thus developed image wastransferred to a transfer paper and fixed so that an image of extremelyexcellent quality was obtained.

EXAMPLE 6

Photosensitive members were prepared by repeating the same procedureunder the same condition as in Example 1 except that the temperature ofthe substrate was varied as shown in Table 1 given below. The preparedphotosensitive members are indicated by Sample Nos. 1-8 in Table 1.

By using the photosensitive meanders, the image formation was carriedout under the same condition as in Example 3 to form images on transferpapers. The obtained results are as shown in Table 1.

As understood from the results, it is necessary to form the a-Si layerat a temperature of the substrate ranging from 50° C. to 350° C. for thepurpose of achieving the object of the present invention.

                                      TABLE 1    __________________________________________________________________________    Sample No.  1  2  3   4  5   6  7  8    __________________________________________________________________________    Substrate temp., °C.                50 100                      150 200                             250 300                                    350                                       400    Image         Charged              ⊕                X  Δ                      Δ                          Δ                             X   X  X  X    quality         polarity              ⊖                Δ                   ⊚                      ⊚                          ⊚                             ∘                                 ∘                                    Δ                                       X    __________________________________________________________________________     Image quality is that of transferred image.     ⊚ Very good; ∘ Good; Δ Acceptable for     practical use; X Poor

EXAMPLE 7

Photosensitive members were prepared by repeating the same procedure andcondition as in Example 3 except that the temperature of the substratewas varied as shown in Table 2 given below. The prepared photosensitivemembers are indicated. by Sample Nos. 9-16 in Table 2.

By using the photosensitive members, the image formation was carried outby using the same procedure and condition as in Example 3 to form imageson transfer papers. The obtained results are as shown in Table 2.

As understood from the results, it is necessary to form the a-Si layerat a temperature of the substrate ranging from 50° C. to 350° C. for thepurpose of achieving the object of the present invention.

                                      TABLE 2    __________________________________________________________________________    Sample No.  9  10 11  12 13  14 15 16    __________________________________________________________________________    Substrate temp., °C.                50 100                      150 200                             250 300                                    350                                       400    Image         Charged              ⊕                Δ                   ⊚                      ⊚                          ⊚                             ∘                                 ∘                                    Δ                                       X    quality         polarity              ⊖                Δ                   ⊚                      ⊚                          ⊚                             ∘                                 ∘                                    Δ                                       X    __________________________________________________________________________     Image quality is that of transferred image.     ⊚ Very good; ∘ Good; Δ Acceptable for     practical use; X Poor

EXAMPLE 8

Photosensitive members were prepared by repeating the same procedure andcondition as in Example 4 except that the temperature of the substratewas varied as shown in Table 3 given below. The prepared photosensitivemembers are indicated by Sample Nos. 17-24 in Table 3.

By using the photosensitive members, the image formation was carried outby employing the same procedure and condition as in Example 4 to formimages on transfer papers. The obtained results are as shown in Table 3.

As understood from the results, it is necessary to form the a-Si typelayer at a temperature of the substrate ranging from 50° C. to 350° C.for the purpose of achieving the object of the present invention.

                                      TABLE 3    __________________________________________________________________________    Sample No.  17 18 19  20 21  22 23 24    __________________________________________________________________________    Substrate temp., °C.                50 100                      150 200                             250 300                                    350                                       400    Image         Charged              ⊕                Δ                   ⊚                      ⊚                          ⊚                             ∘                                 ∘                                    Δ                                       X    quality         polarity              ⊖                X  Δ                      Δ                          Δ                             X   X  X  X    __________________________________________________________________________     Image quality is that of transferred image.     ⊚ Very good; ∘ Good; Δ Acceptable for     practical use; X Poor

EXAMPLE 9

A cylinder made of aluminum having a thickness of 2 mm and a size of150.sup.φ mm×300 mm was disposed in a deposition apparatus for glowdischarge shown in FIG. 3 so that it might rotate freely, and a heaterwas mounted so as to heat the cylinder from the inside of the cylinder.

The air in a deposition chamber 10 was evacuated by opening fully a mainvalve 29 to bring the chamber to a vacuum degree of about 5×10⁻⁵ Torr.The heater 13 was ignited to heat uniformly the cylinder to 150° C.simultaneously with the cylinder being rotate at a speed of threerevolutions per minute, and the cylinder was kept at that temperature. Asubsidiary valve 28 was fully opened, and subsequently a valve 25 of abomb 16 to which Ar was charged and a valve 26 of a bomb 17 which wasfilled with SiH₄ were also opened fully, and thereafter, flow amountcontrolling valves 22, 23 were gradually opened so that Ar gas and SiH₄gas were introduce into the deposition chamber 10 from the bombs 16, 17.At that time, the vacuum degree in the deposition chamber 10 was broughtto and kept at about 0.075 Torr. by regulating the main valve 29.Further, the flow amount of the SiH₄ gas was adjusted to 10% by volumebased on that of the Ar gas.

After fully opening of a valve 27 of a bomb 18, to which B₂ H₆ wascharged, a flow amount controlling valve 24 was gradually opened while aflow meter 21 was carefully observed, to adjust the flow amount of B₂ H₆gas to 10⁻⁵ % by volume based on that of the SiH₄ gas, therebyintroducing the B₂ H₆ gas into the deposition chamber 10. Also at thattime, the main valve 29 was regulated to bring the vacuum degree in thedeposition chamber 10 to about 0.075 Torr.

A high frequency power source 14 was switched on to apply a highfrequency voltage of 13.56 MHz between electrodes 15 and 15' so that aglow discharge was caused, thereby depositing and forming an a-Si typephotoconductive layer on the cylinder substrate. At that time, the glowdischarge was initiated with an electric current density of about 3mA/cm² and a voltage of 1,500 V. Further, the growth rate of the a-Sitype layer was about 2.5 angstroms per second and the deposition waseffected for 23 hours and further the thus formed a-Si type layer had athickness of 20 microns.

After completion of the deposition, while the main valve 29, subsidiaryvalve 28, flow amount controlling valves 22 and 23, valves 25 and 26were closed, a valve 30 was opened to break the vacuum state in thedeposition chamber 10. The prepared electrophotographic photosensitivemember was taken out from the deposition apparatus.

To the a-Si type photoconductive layer surface of the photosensitivemember was applied negative corona discharge with a power source voltageof 5,500 V in a dark place. The image exposure was conducted in anexposure quantity of 20 lux·sec. to form an electrostatic image, whichwas then developed with a positively charged toner in accordance withthe cascade method. The developed image was transferred to a transferpaper and then fixed so that an extremely sharp image was obtained.

The image forming process as mentioned above was repeatedly carried outin order to test the durability of the photosensitive member. As aresult, the image on the transfer paper obtained when such process wasrepeated ten thousand (10,000) times was extremely good in the quality.Although such image was compared with the first image on a transferpaper obtained at the time of the initial operation of the image formingprocess, no different was observed therebetween. Therefore, it was foundthat the photosensitive member is extremely excellent in the durability.In addition, the blade cleaning was effected in cleaning thephotosensitive member after the transferring step, the blade beingformed of urethane rubber.

Further, the foregoing image forming process was repeated under the samecondition except that positive corona discharge was applied with a powersource voltage of 6,000 V to the photosensitive member and a negativelycharged toner was used for the development. The thus obtained imageformed on the transfer paper had an image density lower than that of theimage obtained in the foregoing image forming process using negativecorona discharge. As a result, it was recognized that the photosensitivemember prepared in this example depends upon the polarity to be charged.

EXAMPLE 10

Electrophotographic photosensitive members, which are indicated bySample Nos. 25-29 in Table 4 given below, were prepared by conductingthe same procedure under the same condition as in Example 3 except thatthe flow amount of the B₂ H₆ gas based on that of the SiH₄ gas wasvaried in order to control the amount of the boron (B) doped into thea-Si type layer to various values as shown in Table 4.

The image formation was effected by employing the photosensitive membersunder the same condition as in Example 3 to obtain images on transferpapers. The results are shown in Table 4. As clear from the results,with respect to practically usable photosensitive member, it is desiredto dope the a-Si type layer with boron (B) in an amount of 10⁻⁶ -10⁻³atomic percent.

                  TABLE 4    ______________________________________    Sample No.   25       26      27    28   29    ______________________________________    Doping amount                 10.sup.-6                          10.sup.-5                                  10.sup.-4                                        10.sup.-3                                             1    of B, atomic %    Image quality                 ∘                          ⊚                                  ⊚                                        ∘                                             X    ______________________________________     Image quality is that of transferred image.     ⊚ Very good; ∘ Good; X Poor

EXAMPLE 11

In accordance with the procedure described below, an electrophotographicphotosensitive member was prepared by using an apparatus as shown inFIG. 4, and the image forming treatment was applied to thephotosensitive member.

An aluminum substrate of 1 mm in thickness and 10 cm×10 cm in size wascleaned in such a manner that the surface of the substrate was treatedwith a 1% solution of NaOH and sufficiently washed with water and dried,and then Mo was deposited to this substrate to about 1,000 angstroms inthickness. This substrate was firmly fixed at a predetermined positionin a fixing member 33 placed in a deposition chamber 31 so that thesubstrate was kept apart from a heater 34 by about 1.0 cm. Also, thesubstrate was parted from a target 35 of polycrystalline silicon havinga purity of 99.999% by about 8.5 cm.

The air in the deposition chamber 31 was evacuated to bring the chamberto a vacuum degree of about 1×10⁻⁶ Torr. The heater 34 was ignited toheat uniformly the substrate to 150° C., and the substrate was kept atthis temperature. A valve 45 was fully opened, and subsequently a valve40 of a bomb 38 was also opened fully, and thereafter, a flow amountcontrolling valve 44 was gradually opened so that H₂ gas was introducedinto the deposition chamber 31 from the bomb 38. At that time, thevacuum degree in the deposition chamber 31 was brought to and kept atabout 5.5×10⁻⁴ Torr. by regulating the main valve 46.

Subsequently, after fully opening of a valve 39, a valve 39, a flowamount controlling valve 43 was gradually opened with a flow meter 41being carefully observed, to introduce Ar gas into the depositionchamber 31 in which the vacuum degree was adjusted to 5×10⁻³ Torr.

A high frequency power source 36 was switched on to apply a highfrequency voltage of 13.56 MHz, 1 KV between the aluminum substrate andpolycrystalline silicon target so that a discharge was caused, therebystarting formation of an a-Si layer on the aluminum substrate. Thisoperation was conducted continuously with a growth rate of the a-Silayer being controlled to about two angstroms per second for 30 hours.The thus formed a-Si layer was 20 microns in thickness.

To the thus prepared electrophotographic photosensitive member wasapplied negative corona discharge with a power source voltage of 5,500 Vin a dark place. The image exposure was conducted in an exposurequantity of 15 lux·sec. to form an electrostatic image, which was thendeveloped with a positively charged toner in accordance with the cascademethod. The developed image was transferred to a transfer paper and thenfixed so that an extremely sharp image was obtained.

EXAMPLE 12

Electrophotographic photosensitive members, which are indicated bySample Nos. 30-36 in Table 5 given below, were prepared by conductingthe same procedure under the same condition as in Example 11 except thatthe flow amount of the H₂ gas based on that of the Ar gas was varied inorder to control the amount of the hydrogen (H) doped into the a-Si typelayer to various values as shown in Table 5.

The image formation was effected by employing the photosensitive membersunder the same condition as in Example 11 to obtain images on transferpapers. The results are shown in Table 5. As clear from the results,with respect to practically usable photosensitive member, it is desiredto dope the a-Si type layer with H in an amount of 10-40 atomic percent.

                  TABLE 5    ______________________________________    Sample No.   30     31     32   33   34   35   36    ______________________________________    Doping amount                 5      10     15   25   30   40   50    of H, atomic %    Image quality                 X      ∘                               ⊚                                    ⊚                                         ⊚                                              ∘                                                   X    ______________________________________     Image quality is that of transferred image.     ⊚ Very good; ∘ Good; X Poor

EXAMPLE 13

The electrophotographic photosensitive members prepared in Examples 1, 3and 4 were each allowed to stand in an atmosphere of high temperatureand humidity, i.e., at a temperature of 40° C. and relative humidity of90 RH %. After the lapse of 96 hours, the photosensitive members weretaken out into an atmosphere at a temperature of 23° C. and relativehumidity of 50 RH %. Immediately thereafter, the same image formingprocesses as in Examples 1, 3 and 4 were conducted under the samecondition by using the photosensitive members to obtain images ofsharpness and good quality on transfer paper. This result showed thatthe photosensitive member of the present invention is very excellentalso in moisture resistance.

EXAMPLE 14

An electrophotographic photosensitive member was prepared in the samemanner as that in Example 1. To the member was applied negative coronadischarge at a voltage of 6,000 V in a dark place and image exposure wasthen conducted in an exposure quantity of 20 lux·sec. to form anelectrostatic image, which was then developed with a liquid developercontaining a chargeable toner dispersed in a solvent of an isoparaffintype hydrocarbon. The developed image was transferred to a transferpaper followed by fixing. The fixed image was extremely high in theresolution and of good image quality with sharpness.

Further, the above described image forming process was repeated in orderto test the solvent resistance, in other words, liquid developerresistance of the photosensitive member. The above-mentioned image onthe transfer paper was compared with an image on a transfer paperobtained when the image forming process was repeated ten thousand(10,000) times. As a result, no difference was found therebetween, whichshowed that the photosensitive member of the present invention isexcellent in the solvent resistance.

In addition, as the manner of cleaning the photosensitive member surfaceeffected in the image forming process, the blade cleaning method wasused, the blade being formed of urethane rubber.

EXAMPLE 15

In accordance with the procedure described below, an electrophotographicphotosensitive member was prepared by using a depositing apparatus forglow discharge as illustrated in FIG. 5 and the image forming processwas carried out by employing the photosensitive member.

An aluminum substrate 48 having a size of 10 cm×10 cm×1 mm alreadycleaned by the same surface treatment as in Example 1 was firmlydisposed at a fixed position in a fixing member 49 placed in adeposition chamber 47 so that the substrate might be kept apart from aheater 50 by 1.0 cm or so.

A main valve 66 and subsidiary valve 65 were fully opened to evacuatethe air in the deposition chamber 47 and mixing tank 68, thereby bringthem to the vacuum degree of about 5×10⁻⁵ Torr. This is shown by labelA↓ in FIG. 5. The heater 50 was then ignited to heat uniformly thealuminum substrate to 150° C., the substrate being kept at thattemperature.

The subsidiary valve 65 was then closed, while a valve 62 of a bomb 53which was filled up with Ar and valve 63 of a bomb 54 containing SiH₄charged thereto were fully opened. Flow amount controlling valves 59, 60for the gas bombs 53, 54 were regulated with flow meters 56, 57 beingobserved so that Ar gas and SiH₄ gas were fed to the mixing tank 68 at aratio by volume of Ar:SiH₄ =10:1. While the flow amount controllingvalves 59, 60 were then closed, the subsidiary valve 65 was graduallyopened to introduce a gas mixture of Ar and SiH₄ gases into thedeposition chamber 47. At that time, the main valve 66 was regulated toretain the vacuum degree in the deposition chamber 47 at about 0.075Torr.

Subsequently, a high frequency power source 51 was switched on to applya high frequency voltage of 13.56 MHz to inductance type coil 52. As aresult, a glow discharge took place, thereby forming an a-Si typephotoconductive layer on the aluminum substrate by deposition. At thattime, the high frequency power was about 50 W and the growth rate of thelayer about three angstroms per second. Further, the period of time forthe deposition was 20 hours and the formed a-Si type layer had athickness of about 20 microns.

To the a-Si type photoconductive layer surface of the thus preparedphotosensitive member was applied negative corona discharge with asource voltage of 5,500 V in a dark place. The image exposure was theneffected in an exposure quantity of 15 lux·sec. to form an electrostaticimage, which was then developed with a positively charged toner by thecascade method. The developed image was transferred to a transfer paperand fixed. As a result, an image of high resolution with very sharpnesswas obtained.

EXAMPLE 16

In accordance with the procedure described below, an electrophotographicphotosensitive member was prepared by using an apparatus as illustratedin FIG. 5 and the image forming process was carried out by employing thephotosensitive member.

An aluminum substrate having a thickness of 1 mm and size of 10 cm×10 cmalready was cleaned in such a manner that the surface was treated with a1% solution of NaOH, sufficiently washed with water and dried. Thissubstrate was firmly disposed at a predetermined position in a fixingmember 49 placed in a deposition chamber 47 so that the substrate mightbe kept apart from a heater 50 by 1.0 cm or so.

A main valve 66 and subsidiary valve 65 were fully opened to evacuatethe air in the deposition chamber 47 and mixing tank 68, thereby bringthem to the vacuum degree of about 5×10⁻⁵ Torr. The heater 50 was thenignited to heat uniformly the aluminum substrate to 150° C., thesubstrate being kept at that temperature.

The subsidiary valve 65 was them closed, while a valve 62 of a bomb 53and valve 63 of a bomb 54 were fully opened. Flow amount controllingvalves 59, 60 were gradually opened with flow meters 56, 57 beingobserved so that Ar gas and SiH₄ gas were introduced from the bombs 53,54, respectively, to the mixing tank 68 at a ratio by volume of Ar:SiH₄=10:1. After a predetermined amount of the Ar and SiH₄ gases were fed tothe tank 68, the flow amount controlling valves 59, 60 were then closed.

Next, a valve 64 of a bomb 55 was fully opened, and thereafter a flowamount controlling valve 61 was gradually opened to introduce B₂ H₆ gasinto the mixing tank 68 from the bomb 55 while the flow amount of the B₂H₆ gas was controlled to a ratio by volume of SiH₄ :B₂ H₆ =1:3×10⁻⁵.After a predetermined amount of the B₂ H₆ gas was fed to the tank 68,the valve 61 was closed. Then, the subsidiary valve 65 was graduallyopened to introduce a gas mixture of Ar, SiH₄ and B₂ H₆ gases from thetank 68 into the deposition chamber 47. At this time, the main valve 66was regulated to bring the vacuum degree in the deposition chamber 47 to0.075 Torr.

Subsequently, a high frequency power source 51 was switched on to applya high frequency voltage of 13.56 MHz to inductance type coil 52. As aresult, a glow discharge took place, thereby forming an a-Si typephotoconductive layer on the aluminum substrate by deposition. At thattime, the high frequency power was about 50 W and the growth rate of thelayer about 4 angstroms per second. Further, the period of time for thedeposition was 15 hours and the formed a-Si type layer had a thicknessof about 20 microns.

After completion of the deposition, the main valve 66 and subsidiaryvalve 65 were closed, but the valve 67 was opened to break the vacuumstate in the deposition chamber 47. The prepared photosensitive memberwas taken out from the apparatus.

To the a-Si type photoconductive layer surface of the thus preparedphotosensitive member was applied negative corona discharge with asource voltage of 5,500 V in a dark place. The image exposure was theneffected in an exposure quantity of 20 lux·sec. to form an electrostaticimage, which was then developed with a positively charged toner by thecascade method. The developed image was transferred to a transfer paperand fixed. As a result, an image with very sharpness was obtained.

The image forming process as mentioned above was repeatedly carried outin order to test the durability of the photosensitive member. As aresult, the image on the transfer paper obtained when such process wasrepeated ten thousand (10,000) times was extremely good in the quality.Although such image was compared with the first image on a transferpaper obtained at the time of the initial operation of the image formingprocess, no different was observed therebetween. Therefore, it was foundthat the photosensitive member is very excellent in the durability. Inaddition, the blade cleaning was effected in cleaning the photosensitivemember after the transferring step and the blade was formed of urethanerubber.

EXAMPLE 17

An electrophotographic photosensitive member was prepared by using thesame procedure and condition as in Example 11 except that in place ofthe H₂, SiH₄ was charged to the bomb 38 and SiH₄ gas was introduced intothe deposition chamber 31.

The image formation was effected by using the photosensitive member inthe same manner as in Example 11 under the equivalent condition. Theobtained result was similar to that in Example 11.

EXAMPLE 18

In accordance with the procedure described below, an electrophotographicphotosensitive member was prepared by using an apparatus as shown inFIG. 3, and the image forming treatment was applied to thephotosensitive member.

An aluminum substrate of 1 mm in thickness and 10 cm×5 cm in size wascleaned in such a manner that the surface of the substrate was treatedwith a 1% solution of NaOH and sufficiently washed with water and thendried. This substrate was firmly fixed at a predetermined position in afixing member 12 placed in a deposition chamber 10 for glow discharge sothat the substrate was kept apart from a heater 13 equipped to thefixing member 12 by about 1.0 cm.

The air in the deposition chamber 10 was evacuated by opening fully amain valve 29 to bring the chamber to a vacuum degree of about 5×10⁻⁵Torr. A subsidiary valve 28 was fully opened, and subsequently a valve25 of a bomb 16 was also opened fully, and thereafter, a flow amountcontrolling valve 22 was gradually opened so that Ar gas was introducedinto the deposition chamber 10 from the bomb 16. At that time, theinside pressure in the deposition chamber 10 was brought to and kept atabout 0.075 Torr.

A high frequency power source 14 was switched on to apply a highfrequency voltage of 13.56 MHz between electrodes 15 and 15' so that aglow discharge was caused, thereby cleaning the surface of the aluminumsubstrate. At that time, the glow discharge was initiated with a currentdensity of about 0.5 mA/cm² and a voltage of 500 V. After completion ofthe cleaning treatment, the subsidiary valve 28, valve 25 and flowamount controlling valve 22 were closed.

Subsequently, in accordance with the procedure and condition used inExample 1, an a-Si layer of about 20 microns in thickness was formed onthe aluminum substrate to obtain an electrophotographic photosensitivemember.

The photosensitive member was used to the image forming process in thesame manner and condition as in Example 1 to obtain an image transferredto a paper. Similar result to that in Example 1 was obtained. Further,as to the durability of the photosensitive member, the same result wasobtained.

EXAMPLE 19

An electrophotographic photosensitive member having an a-Si was preparedby employing the same procedure and condition as in Example 1.Deposition of Ta₂ O₅ to the surface of the photoconductive layer waseffected by the electron beam deposition to form an anti-reflectionlayer of 70 milli microns in thickness.

The image forming process described in Example 1 was repeated by usingthe thus prepared photosensitive member. As a result, it was found thatthe photosensitive member requires an exposure quantity of only about 12lux·sec. to attain a transferred image density similar to that obtainedin Example 1.

EXAMPLE 20

In accordance with the procedure described below, an electrophotographicphotosensitive member was prepared by using an apparatus as shown inFIG. 3, and the image forming treatment was applied to thephotosensitive member.

An aluminum substrate of 1 mm in thickness and 10 cm×10 cm in size wascleaned in such a manner that the surface of the substrate was treatedwith a 1% solution of NaOH and sufficiently washed with water and thendried. This substrate was firmly fixed at a predetermined position in afixing member 12 placed in a deposition chamber 10 for glow discharge sothat the substrate was kept apart from a heater 13 by about 1.0 cm.

The air in the deposition chamber 10 was evacuated by opening fully amain valve 29 to bring the chamber to a vacuum degree of about 5×10⁻⁵Torr. The heater 13 was ignited to heat uniformly the aluminum substrateto 150° C., and the substrate was kept at this temperature. A subsidiaryvalve 28 was fully opened, and subsequently a valve 25 of a bomb 16 anda valve 26 of a bomb 17 were also opened fully, and thereafter, flowamount controlling valves 22, 23 were gradually opened so that Ar gasand SiH₄ gas were introduced into the deposition chamber 10 from thebombs 16 and 17, respectively. At that time, the vacuum degree in thedeposition chamber 10 was brought to and kept at about 0.075 Torr byregulating the main valve 29.

A high frequency power source 14 was switched on to apply a highfrequency voltage of 13.56 MHz between electrodes 15 and 15' so that aglow discharge was caused, thereby depositing and forming an a-Si typephotoconductive layer on the aluminum substrate. At that time, the glowdischarge was initiated with an electric current density of about 5mA/cm² and a voltage of 2,000 V. Further, the growth rate of the a-Sitype layer was about 4 angstroms per second and the deposition waseffected for 15 hours and further the thus formed a-Si type layer had athickness of 20 microns.

After completion of the deposition, while the main valve 29, valves 25and 26, flow amount controlling valves 22 and 23, and subsidiary valve28 were closed, a valve 30 was opened to break the vacuum state in thedeposition chamber 10. The prepared photosensitive member was then takenout from the deposition chamber.

To the a-Si type photoconductive layer surface of the photosensitivemember was applied negative corona discharge with a source voltage of5,500 V in a dark place. The image exposure was conducted in an exposurequantity of 15 lux·sec. to form an electrostatic image, which was thendeveloped with a positively charged toner in accordance with the cascasemethod. The developed image was transferred to a transfer paper and thenfixed so that a sharp image with a high resolution was obtained.

The image forming-process as mentioned above was repeatedly carried outin order to test the durability of the photosensitive member. As aresult, the image on the transfer paper obtained when such process wasrepeated ten thousand (10,000) times was extremely good in the quality.Although such image was compared with the first image on a transferpaper obtained at the time of the initial operation of the image formingprocess, no different was observed therebetween. Therefore, it was foundthat the photosensitive member is excellent in the corona dischargingresistance, abrasion resistance, cleaning property and the like andshows extremely excellent durability. In addition, the blade cleaningwas effected in cleaning the photosensitive member after thetransferring step, the blade being formed of urethane rubber.

Further, the foregoing image forming process was repeated under the samecondition except that positive corona discharge was applied with avoltage of 6,000 V to the photosensitive member and negatively chargedtoner was used for the development. The thus obtained image formed onthe transfer paper had an image density lower than that of the imageobtained in the foregoing image forming process using negative coronadischarge.

As a result, it was recognized that the photosensitive member preparedin this example depends upon the polarity to be charged.

EXAMPLE 21

In accordance with the procedure and condition used in Example 20, ana-Si type layer of 20 microns in thickness was formed on the aluminumsubstrate. The structure was taken out from the deposition chamber 10 tothe outside, and polycarbonate resin was then coated onto the a-Si typelayer to form an electrically insulating layer having a thickness of 15microns after drying.

To the insulating layer surface of the electrophotographicphotosensitive member obtained in the above-mentioned manner was appliedpositive corona discharge with a power source voltage of 6,000 V as theprimary charging for 0.2 sec. so that such surface was charged to avoltage of +2,000 V. Negative corona discharging with a voltage of 5,500V was carried out as the secondary charging simultaneously with theimage exposure in an exposure quantity of 15 lux·sec., and the wholesurface of the photosensitive member was then exposed uniformly to forman electrostatic image. This image was developed with a negativelycharged toner by the cascade method, and the thus developed image wastransferred to a transfer paper and fixed so that an image of extremelyexcellent quality was obtained.

EXAMPLE 22

In the following manner similar to that in Example 20, anelectrophotographic photosensitive member was prepared by using theapparatus as illustrated in FIG. 3 and the image forming treatment wasapplied to the photosensitive member.

An aluminum substrate having a thickness of 1 mm and a size of 10 cm×10cm was first treated with a 1% solution of NaOH and sufficiently washedwith water and dried to clean the surface of the substrate. Thissubstrate was firmly disposed at a fixed position in a fixing member 12placed in a deposition chamber 10 for glow discharge so that it might bekept apart from a heater 13 positioned in the fixing member 12 by about1.0 cm.

A main valve 29 was fully opened to evacuate the air in the depositionchamber 10 so that the vacuum degree in the chamber was adjusted toabout 5×10⁻⁵ Torr. The heater 13 was ignited to heat uniformly thealuminum substrate to 150° C., the substrate being kept at thattemperature. Then, a subsidiary valve 28 was first opened fully, andsuccessively a valve 25 of a bomb 16 containing Ar charged thereto and avalve 26 of a bomb 17 containing SiH₄ charged thereto were fully opened.Thereafter, the flow amount controlling valves 22 and 23 were graduallyopened so that Ar gas and SiH₄ gas were introduced into the depositionchamber 10 from the bombs 16 and 17, respectively. At this time, thevacuum degree in the deposition chamber 10 was kept at about 0.075 Torr.by regulating the main valve 29, and while flow meters 19 and 20 werecarefully observed, the flow amount controlling valves 22 and 23 wereregulated to control the flow amount of the gases so that the flowamount of the SiH₄ gas might be 10% by volume based on that of the Argas.

A valve 27 of a bomb 18 containing B₂ H₆ charged thereto was fullyopened and then a flow amount controlling valve 24 was slowly opened tointroduce B₂ H₆ gas into the deposition chamber 10 while the flow amountof the gas was controlled so that it might be 5×10⁻³ % by volume basedon the flow amount of the SiH₄ gas. In this case, the main valve 29 wasregulated to retain the vacuum degree in the deposition chamber 10 to0.075 Torr

Subsequently, a high frequency power source 14 was switched on in orderto apply a high frequency voltage of 13.56 MHz between electrodes 15 and15' to give rise to the glow discharge so that an a-Si typephotoconductive layer is formed on the aluminum substrate by thedeposition. At the time of the glow discharge, the current density wasabout 3 mA/cm² and the voltage 1,500 V. Further, the growth rate of thea-Si type layer was about 4 angstroms/sec., the period of time for thedeposition 15 hours, and the thickness of the a-Si type layer 20microns. After completion of the deposition, the main valve 29,subsidiary valve 28, flow amount controlling valves 22, 23, 24, andvalves 25, 26, 27 were closed, but the valve 30 was opened to break thevacuum state in the deposition chamber 10. Then, the electrophotographicphotosensitive member obtained in the above mentioned manner was takenout from the apparatus.

To the a-Si type photoconductive layer surface of the photosensitivemember was applied negative corona discharge with a voltage of 5,500 Vin a dark place. The image exposure was conducted in an exposurequantity of 20 lux·sec. to form an electrostatic image, which was thendeveloped with a positively charged toner in accordance with the cascademethod. The developed image was transferred to a transfer paper and thenfixed so that an extremely sharp image was obtained.

The image forming process as mentioned above was repeatedly carried outin order to test the durability of the photosensitive member. As aresult, the image on the transfer paper obtained when such process wasrepeated ten thousand (10,000) times was extremely good in the quality.Although such image was compared with the first image on a transferpaper obtained at the time of the initial operation of the image formingprocess, no different was observed therebetween. Therefore, it was foundthat the photosensitive member is very excellent in the durability. Inaddition, the blade cleaning was effected in cleaning the photosensitivemember after the transferring step, the blade being formed of urethanerubber.

Further, positive corona discharge with a power source voltage of 6,000V was applied to the photosensitive member in a dark place and the imageexposure was conducted in an exposure quantity of 20 lux·sec. to form anelectrostatic image. This electrostatic image was developed with anegatively charged toner by the cascade method. The developed image wasthen transferred to a transfer paper and fixed so that an image withextreme sharpness was obtained.

It was found from this result and the before-said result that thephotosensitive member obtained in this example does not havedependability to the charged polarity, but it possesses properties of aphotosensitive member which can be advantageously used with bothpolarities to be charged.

EXAMPLE 23

The same procedure as in Example 22 was repeated except that the flowamount of the B₂ H₆ gas was adjusted to 5×10⁻⁴ % by volume based on theflow amount of the SiH₄ gas, to prepare an electrophotographicphotosensitive member having an a-Si type photoconductive layer of 20microns in thickness on the aluminum substrate.

In accordance with the same condition and manner as in Example 3, theimage forming process was carried out by using the obtainedphotosensitive member to form an image on a transfer paper. As a result,the image formed by the process using positive corona discharge wasexcellent in quality and very sharp as compared with that obtained bythe process employing negative corona discharge.

It is recognized from the result that the photosensitive member of thisexample depends upon the polarity to be charged. In addition, thispolarity dependability is contrary to that of the photosensitive memberobtained in Example 1.

EXAMPLE 24

In accordance with the procedure and condition used in Example 23, ana-Si type layer of 20 microns in thickness was formed on the aluminumsubstrate. The structure was taken out from the deposition chamber 10,and polycarbonate resin was then coated onto the a-Si type layer to forman electrically insulating layer having a thickness of 15 microns afterdrying.

To the insulating layer surface of the electrophotographicphotosensitive member obtained in the above-mentioned manner was appliednegative corona discharge with a power source voltage of 6,000 V as theprimary charging for 0.2 sec. so that such surface was charged to avoltage of -2,000 V. Positive corona discharging with a voltage of 5,500V was carried out as the secondary charging simultaneously with theimage exposure in an exposure quantity of 15 lux·sec., and the wholesurface of the photosensitive member was then exposed uniformly to forman electron static image. This image was developed with a positivelycharged toner by the cascade method, and the thus developed image wastransferred to a transfer paper and fixed so that an image of extremelyexcellent quality was obtained.

EXAMPLE 25

Photosensitive members were prepared by repeating the same procedure andcondition as in Example 20 except that the temperature of the substratewas varied as shown in Table 6 given below. The prepared photosensitivemembers are indicated by Sample Nos. 37-44 in Table 6.

By using the photosensitive members, the image formation was carried outby employing under the same manner and condition as in Example 22 toform images on transfer papers. The obtained results are as shown inTable 6.

As understood from the results, it is necessary to form the a-Si typelayer at a temperature of the substrate ranging from 50° C. to 350° C.for the purpose of achieving the object of the present invention.

                                      TABLE 6    __________________________________________________________________________    Sample No.  37 38 39  40 41  42 43 44    __________________________________________________________________________    Substrate temp. °C.                50 100                      150 200                             250 300                                    350                                       400    Image         Charged              ⊕                X  Δ                      Δ                          Δ                             X   X  X  X    quality         polarity              ⊖                Δ                   ⊚                      ⊚                          ⊚                             ∘                                 ∘                                    Δ                                       X    __________________________________________________________________________     Image quality is that of transferred image.     ⊚ Very good; ∘ Good; Δ Acceptable for     practical use; X Poor

EXAMPLE 26

Photosensitive members were prepared by repeating the same procedure andcondition as in Example 22 except that the temperature of the substratewas varied as shown in Table 7 given below. The prepared photosensitivemembers are indicated by Sample Nos. 45-52 in Table 7.

By using the photosensitive members, the image formation was carried outunder the same condition as in Example 22 to form images on transferpapers. The obtained results are as shown in Table 7.

As understood from the results, it is necessary to form the a-Si typelayer at a temperature of the substrate ranging from 50° C. to 350° C.for the purpose of achieving the object of the present invention.

                                      TABLE 7    __________________________________________________________________________    Sample No.    45 46 47 48  49 50 51 52    __________________________________________________________________________    Substrate temp. °C.                  50 100                        150                           200 250                                  300                                     350                                        400    Image         Charged               ⊕                  Δ                     ⊚                        ⊚                           ⊚                               ∘                                  ∘                                     Δ                                        X    quality         polarity               ⊖                  Δ                     ⊚                        ⊚                           ⊚                               ∘                                  ∘                                     Δ                                        X    __________________________________________________________________________     Image quality is that of transferred image.     ⊚ Very good; ∘ Good; Δ Acceptable for     practical use; X Poor

EXAMPLE 27

Photosensitive members were prepared by repeating the same procedure andcondition as in Example 23 except that the temperature of the substratewas varied as shown in Table 8 given below. The prepared photosensitivemembers are indicated by Sample Nos. 53-60 in Table 8.

By using the photosensitive members, the image formation was carried outunder the same condition as in Example 23 to form images on transferpapers. The obtained results are as shown in Table 8.

As understood from the results, it is necessary to form the a-Si typelayer at a temperature of the substrate ranging from 50° C. to 350° C.for the purpose of achieving the object of the present invention.

                                      TABLE 8    __________________________________________________________________________    Sample No.    53 54 55 56  57 58 59 60    __________________________________________________________________________    Substrate temp., °C.                  50 100                        150                           200 250                                  300                                     350                                        400    Image         Charged               ⊕                  Δ                     ⊚                        ⊚                           ⊚                               ∘                                  ∘                                     Δ                                        X    quality         polarity               ⊖                  X  Δ                        Δ                           Δ                               X  X  X  X    __________________________________________________________________________     Image quality is that of transferred image.     ⊚ Very good; ∘ Good; Δ Acceptable for     practical use; X Poor

EXAMPLE 28

Electrophotographic photosensitive members, which are indicated bySample Nos. 61-65 in Table 9 given below, were prepared by conductingthe same procedure under the same condition as in Example 22 except thatthe flow amount of the B₂ H₆ gas based on that of the SiH₄ gas wasvaried in order to control the amount of the boron (B) doped into thea-Si type layer to various values as shown in Table 9.

The image formation was effected by employing the photosensitive membersunder the same condition as in Example 22 to obtain images on transferpapers. The results are shown in Table 9. As clear from the results,with respect to practically usable photosensitive member, it is desiredto dope the a-Si type layer with boron (B) in an amount of 10⁻⁶ -10⁻³atomic percent.

                  TABLE 9    ______________________________________    Sample No,  61      62      63     64    65    ______________________________________    Doping amount                10.sup.-6                        10.sup.-5                                10.sup.-4                                       10.sup.-3                                             1    of B, atomic %    Image quality                ∘                        ⊚                                ⊚                                       ∘                                             X    ______________________________________     Image quality is that of transferred image.     ⊚ Very good; ∘ Good; X Poor

EXAMPLE 29

The photosensitive members prepared in Examples 20, 22 and 23 were eachallowed to stand in an atmosphere of high temperature and humidity,i.e., at a temperature of 40° C. and relative humidity of 90 RH %. Afterthe lapse of 96 hours, the photosensitive members were taken out into anatmosphere at a temperature of 23° C. and relative humidity of 50 RH %.Immediately thereafter, the same image forming processes as in Examples20, 22 and 23 were conducted under the same condition by using thephotosensitive members to obtain images of sharpness and good quality.This result showed that the photosensitive member of the presentinvention is very excellent also in moisture resistance.

EXAMPLE 30

An electrophotographic photosensitive member was prepared in the samemanner as that in Example 20. To the member was applied negative coronadischarge with a power source voltage of 6,000 V in a dark place and theimage exposure was then conducted in an exposure quantity of 20 lux·sec.to form an electrostatic image, which was then developed with a liquiddeveloper containing a chargeable toner dispersed in a solvent of anisoparaffin type hydrocarbon. The developed image was transferred to atransfer paper followed by fixing. The fixed image was extremely high inthe resolution and of good image quality with sharpness.

Further, the above described image forming process was repeated in orderto test the solvent resistance, in other words, liquid developerresistance of the photosensitive member. The foregoing image on thetransfer paper was compared with an image on a transfer paper obtainedwhen the image forming process was repeated ten thousand (10,000) times.As a result, no difference was found therebetween, which showed that thephotosensitive member of the present invention is excellent in thesolvent resistance.

In addition, as the manner of cleaning the photosensitive member surfaceeffected in the image forming process, the blade cleaning method wasused, the blade being formed of urethane rubber.

EXAMPLE 31

An electrophotographic photosensitive member was prepared by using thesame procedure and condition as in Example 1 except that the temperatureof the aluminum substrate was continuously raised from 100° C. to 300°C. for the duration between the start of the a-Si layer formation andthe completion thereof.

The same image forming process as in Example 1 was applied to the thusprepared photosensitive member. It was found that the photosensitivemember is excellent in light fatigue resistance as compared with that ofExample 1. As to the other properties, similar results were obtained.

EXAMPLE 32

An electrophotographic photosensitive member was prepared by repeatingthe same manner and condition as in Example 1 except that thetemperature of the aluminum substrate was controlled as mentioned below.The substrate temperature was adjusted to 100° C. at the time ofstarting the formation of the a-Si type layer, and then continuouslyraised as the layer grew so that the temperature was adjusted to 300° C.immediately before expiration of the layer forming duration andsubsequently decreased to 280° C. so that the image formation wascompleted.

The same image forming treatment as in Example 1 was conducted by usingthe photosensitive member thus prepared. As a result, the photosensitivemember was excellent in light fatigue resistance as compared with thatobtained in Example 1, and as to other properties, similar results wereobtained.

What we claim is:
 1. An image-forming member for electrophotographycomprising: a substrate for electrophotography and a photoconductivelayer comprising amorphous silicon formed on the substrate, wherein thephotoconductive layer contains 10 to 40 atomic percent of hydrogen atomsand an impurity for controlling conductivity type which is selectedbased on positive or negative polarity of an electrostatic image to beformed, and wherein the content of the impurity is varied in the layerthickness direction.
 2. The member according to claim 1, wherein theimpurity comprises an element of Group IIIA or VA of the Periodic Table.3. The member according to claim 2, wherein the element of Group IIIA ofthe Periodic Table is selected from the group consisting of B, Al, Ga,In and Tl.
 4. The member according to claim 2, wherein the element ofGroup VA of the Periodic Table is selected from the group consisting ofN, P, As, Sb and Bi.
 5. The member according to claim 1, wherein thephotoconductive layer has a thickness of 5 to 80 μm.
 6. The memberaccording to claim 1, further comprising a covering layer on thephotoconductive layer.
 7. The member according to claim 1, furthercomprising a barrier layer between the substrate and the photoconductivelayer.
 8. The member according to claim 7, wherein the barrier layercontains silicon atoms.
 9. A member according to claim 8, wherein thebarrier layer further contains oxygen atoms.